After a short apprenticeship in
Bremen, Krug arrived in
Puerto Rico in 1857 and started work in the international trading company of Lahmayer & Co. (later Schulze & Co.) in
Mayaguez, Puerto Rico. He became partner, and later sole owner of the company. He became vice-consul in Mayaguez of both Germany and Great Britain. Under the influence of his legal advisor Don
Domingo Bello y Espinoza, Krug became an avid collector of plants and insects. He underwrote several collecting expeditions by the zoologist
Juan Gundlach. These collecting activities resulted in a large amount of scientific material, which became part of the Zoological Museum and Ethnographic Museum in Berlin. ==Berlin==